Generally, a user interface used in PC software supports presentation of pages, such that each page appears within a window that opens up on a display screen in response to user operations. The pages and windows are normally simple and practical and without much decoration.
For content creators, however, it counts a lot to amuse or entertain users watching their contents, so that the menus are designed to be presented with various effects. Examples of such effects include an in-effect and an out-effect which are each a sequence of graphics played back in response to a menu call by a user, as an animated introduction or removal of a menu page. An in-effect is played back immediately before a menu page is presented, whereas an out-effect is played back immediately after a menu page is removed.
Suppose, for example, an in-effect is animation in which a character appearing in a main movie transforms into a menu When a user calls a menu during playback of the main movie recorded on a disc which also stores the in-effect, the playback apparatus presents the menu immediately after playback of the in-effect. With this arrangement, it appears to the user, especially to a little child, as if the character is transformed into the menu in response to his operation. This makes the interactive control more attractive and enjoyable even to little children.
It should be noted here that effects provided by conventional disc contents require interruption of AV playback. Each time a menu is called, the AV playback is interrupted to present an effect. Although the effect may at first appear new and attractive, the playback of the same effect over and over with interruption of AV playback is likely to irritate the users.
One way to avoid the above problem is to overlay an in-effect and an out-effect onto the video image. As a result, the in-effect and out-effect are presented without interrupting AV playback, which is desirable in users' point of view. On the other hand, in order for simultaneous playback of the video image and the animated effect, the playback apparatus needs to simultaneously transfer the video stream and the graphics data used for the effect. Such simultaneous transfer requires the playback apparatus to have a large amount of bandwidth. Even for presenting effects without interaction of AV playback, it is unpractical to require a playback apparatus to have such a high bandwidth. Such playback apparatus is very unlikely to be the standard.